Of all the forms of copyright protected works, music is perhaps the most restricted and licensed. Since music was first broadcast on radio, a vast mechanism for licensing music has emerged from the opposing forces of the recording industry and the radio and TV broadcasting industries. This adds to the risk assessment factor and complicates evaluations of fair use as well, since "harm to the market" for the work is a much broader question.
When thinking of using or performing a musical work, consider:
For information on finding music you can safely reuse, see our Legal Sources for Multimedia Projects: Audio guide.